Mysterious ‘warm spot’ breaks records in North Pacific Ocean

North Pacific waters have had their warmest summer on record, according to a BBC analysis of a mysterious marine heatwave that has confounded climate scientists.

Sea surface temperatures between July and September were more than 0.25C above the previous 2022 peak – a large increase over an area roughly ten times the size of the Mediterranean Sea.

Although climate change is known to make marine heat waves more likely, scientists struggle to explain why the North Pacific has been so hot for so long.

But all that extra warmth in the so-called ‘warm spot’ could backfire in the UK, possibly making a colder start to winter more likely, some researchers believe.

“There’s definitely something unusual going on in the North Pacific,” said Zeke Hausfather, a climate scientist at Berkeley Earth, a US research group.

Such a spike in temperatures across such a large region is “quite remarkable,” he added.

The BBC analyzed data from European Climate Service Copernicus to calculate average temperatures between July and September over a large area of ​​the North Pacific Ocean, sometimes known as the “warm spot”.

The region extends from the east coast of Asia to the west coast of North America, the same area used in the previous one scientific research.

The figures show that not only has the region been warming rapidly over the past few decades, but 2025 is significantly higher than recent years.

That the seas are getting hotter is no surprise. Global warming caused by human emissions of carbon dioxide and other gases has already tripled the number of extreme heat days in the world’s oceans, according to research published earlier this year.

But temperatures have been even higher than predicted by most climate models — computer simulations that account for humanity’s carbon emissions.

Analysis of these models by the Berklee Earth band suggests that the sea temperatures observed in the North Pacific in August had less than a 1% chance of occurring in any one year.

Part of the reason is thought to be the natural variability of the weather. This summer, for example, we saw weaker than usual winds. This means that more heat from the summer sun can stay at the sea surface instead of mixing with cooler waters below.

But that can only go so far in explaining the exceptional conditions, according to Dr Hausfater.

“This is certainly not just natural variability,” he said. “Something else is happening here, too.”

One intriguing idea is that a recent change in shipping fuels may be contributing to the warming. Before 2020, dirty motor oil produced large amounts of sulfur dioxide, a gas harmful to human health.

But that sulfur also forms tiny, sun-reflecting particles in the atmosphere known as aerosols that have helped keep a lid on rising temperatures.

So removing this cooling effect in shipping hotspots like the North Pacific can reveal the full impact of human-caused warming.

“Sulfur seems to be the prime candidate for what’s driving this warming in the region,” Dr Hausfater said.

others research suggests that efforts to reduce air pollution in Chinese cities have also played a role in warming the Pacific Ocean.

This dirty air did a similar job to shipping, reflecting sunlight, while cleaning it up could have the unintended consequence of allowing more ocean heating.

The North Pacific marine heat wave is already having weather effects on both sides of the Pacific Ocean, possibly increasing very high summer temperatures in Japan and South Korea and storms in the US.

“In California, we’re seeing surge thunderstorms because the warm ocean waters in the Pacific provide heat and moisture,” said Amanda Maycock, professor of climate dynamics at the University of Leeds.

“In particular, there are things we call atmospheric rivers … bands of air that contain very large amounts of moisture that are fed by ocean waters,” she added.

“So if we have warm ocean waters … they can bring a lot of moisture to land, which then falls as rain or in the winter it can precipitate as snow.”

Long-term weather forecasting is always a challenge, but extreme heat in the North Pacific has the potential to affect the UK and Europe too in the coming months.

This is due to the connections between the weather in different parts of the world, known as teleconnections.

“Although the current warm conditions are in the North Pacific, they can generate wave motions in the atmosphere that can change our weather downstream in the North Atlantic and in Europe,” Prof Maycock said.

“This could favor high pressure conditions over the continent, bringing us more influence from the Arctic where we have colder air,” she added.

“This could be drawn over Europe and bring us colder weather at the start of winter.”

A colder result is by no means certain, as this is a complex area of ​​science. Several other weather patterns are also affecting UK winters, which tend to become milder with climate change.

And a warm North Pacific appears to have different effects later in the winter, favoring milder and wetter conditions in parts of Europe.

Another factor to throw into the mix is ​​what’s going on further south in the eastern tropical Pacific.

There, the surface waters are unusually cool—a classic sign of the meteorological phenomenon known as The girl.

However, La Niña and its warm sibling El Niño are natural patterns research published this week stressed that global warming itself could affect the fluctuations between them.

Weak La Niña conditions are expected to continue for the next several months, according to NOAA, the US science agency.

All other things being equal, La Niña generally increases the risk of a cold start to the UK winter, but also brings a greater chance of a mild end, The weather service says.

“These two drivers in the North and Tropical Pacific will act together this winter,” Prof Maycock said.

“But since La Niña is quite weak this year, the extreme heat in the North Pacific may be more important in predicting the coming winter.”

Additional reporting by Muskin Lidar and Libby Rogers